The present invention relates to a substrate transfer apparatus for transferring a substrate such as a semiconductor wafer and an LCD substrate, and relates to a substrate processing apparatus.
In manufacturing processes of semiconductor devices and LCDs, a substrate is transferred sequentially to each of process sections by use of the substrate transfer apparatus. In each process section, a plurality of substrates are processed simultaneously. For example, in the photolithographic process of a semiconductor device, a wafer is transferred to a coating unit, in which a photoresist coating film is formed on the surface of the wafer, transferred to a light exposure unit, in which the photoresist coating film is pattern-exposed, and transferred to a development unit to develop the pattern-exposed photoresist coating film.
As an example of the transfer apparatus, an apparatus for transferring a wafer while holding it by vacuum-adsorption, is disclosed in Japanese Patent Application KOKAI Publication No. 6-85042. In the conventionally-used apparatuses, a wafer is vacuum-adsorbed by a vacuum chuck at a center portion of the rear surface thereof, so that particles (derived from the vacuum chuck) may possibly attach to the center portion of the rear surface of the wafer. If the wafer having particles attached on the rear surface is loaded into the light exposure unit, the accuracy of alignment between the wafer and an optical lens decreases, with the result that a pattern latent image cannot be formed on the photoresist film with a high accuracy.
On the other hand, the substrate transfer apparatuses disclosed in US Patent Publications Nos. 5,664,254 and 5,700,127 have an arm holder for holding a wafer in contact with a peripheral portion of the rear surface of the wafer. The arm holder has a contact support portion having a self-alignment means which allows the wafer to directly align upon reception. The diameter of the contact support portion of this type is formed slightly larger than that of the wafer. This is made in order to take out the wafer smoothly and securely from a cassette even if the wafer is placed at a position slightly away from a desired setting position in the cassette.
Incidentally, according to the SEMI (Semiconductor Equipment and Material International) standard, a silicon wafers of 200 mm (8 inch) and 300 mm (12 inch) diameter may have allowances (differences in size) of .+-.0.2 mm and .+-.0.5 mm, respectively. On the other hand, according to the JEIDA (Japan Electronic Industry Development Association) standard, a silicon wafer of 200 mm (8 inch) diameter may have an allowance of .+-.0.5 mm (Glade I) or .+-.1.0 mm (Grade II) and a silicon wafer of 300 mm (12 inch) diameter may have an allowance of .+-.0.2 mm. Therefore, the arm holder must have a contact support portion sufficiently large to support the wafer formed within such an allowance. To attain this, in the conventional contact support portion, an additional space clearance is added to the allowance for the wafer size. Consequently, if a wafer formed in a minimum diameter within the allowance range specified by the standard, is supported, a clearance produced between the contact support portion and the wafer results in 2 mm or more.
Since the wafer is loosely held by the arm holder as mentioned, it moves around on the arm holder during the transfer process. It follows that the member of the contact support portion is rubbed with the wafer, possibly producing particles. Furthermore, when the wafer is transferred from the substrate transfer apparatus to another apparatus, alignment operation of the wafer must be repeated again in said another apparatus. More specifically, it is necessary to align the wafer in every process unit and a transfer apparatus of the light exposure apparatus. However, if an alignment means is newly installed to another transfer apparatus, the apparatus is enlarged and complicated, giving a large foot print of the apparatus.